Thus EP 0 930 979 B1 discloses a self-checking banknote which comprises a flexible plastic carrier. The flexible plastic carrier comprises a transparent material and is provided with a clouded sheathing which leaves a clear transparent surface free as a window. Now, a magnification lens is arranged in the flexible window, as a self-verification means. Further provided on the banknote is a microprint region which manifests a small character, a small line or a filigree pattern. Now, to check or inspect the banknote, the banknote is folded and thus the transparent window and the microprint region are brought into overlapping relationship. The magnification lens can now be used to make the microprint visible to the viewer and thus verify the banknote. In that case, magnification of the micropattern which is afforded to the viewer is determined by the clear range of vision (in the case of normally sighted persons 25 cm) and by the focal length of the magnification lens. The banknote configuration proposed in EP 0 930 979 B1 therefore provides that a security feature which is arranged concealed in the banknote is clearly shown by means of a verification means disposed on the banknote.
In addition EP 0 256 176 A1 discloses a bank passbook with an encrypted identification carrier which is printed internally on the rear cover of the book or on a page of the book and has means for authenticity verification in the form of a transparent region. The transparent region is configured as a reading screen for decrypting the encrypted identification character as soon as that screen is superposed with the surface including the encrypted identification character by the book cover being closed.